An exposure apparatus is used, for example, for producing semiconductor devices so that a pattern formed on a reticle which is used as a mask is transferred onto each of shot areas on a wafer with a photoresist having been applied thereto. Those often used as such an exposure apparatus have been hitherto represented by a reduction projection type exposure apparatus (stepper) of the step-and-repeat system (full-wafer exposure system). In recent years, however, a projection exposure apparatus of the so-called slit scan system attracts attention in response to the request to increase an area of an objective transfer pattern without increasing the load on a projection optical system so much, in which an image of a pattern on a reticle is successively transferred onto a wafer to be exposed by synchronously scanning the reticle and the wafer with respect to the projection optical system while a part of the pattern on the reticle being projected onto the wafer through the projection optical system.
Especially, when exposure is performed in accordance with the slit scan system while an image being reduction-projected onto each of a plurality of shot areas on a wafer, movement from a certain shot area to the next shot area is performed in accordance with the stepping system. Accordingly, such an exposure system is also called the step-and-scan system. As having been hitherto known, the step-and-scan system has been developed from an aligner in which a pattern on an entire surface of a reticle is transferred onto an entire surface of a wafer at an equivalent magnification by means of one time of scanning exposure.
Upon the operation of the projection exposure apparatus of the scanning exposure system such as the slit scan system and the step-and-scan system as described above, it is necessary to stably move a reticle stage and a wafer stage respectively for scanning in a state in which they are synchronized in a predetermined positional relationship. For this purpose, for example, the following operation has been hitherto performed. Namely, before the start of scanning, alignment is performed for the reticle stage and the wafer stage. After that, the wafer stage is scanned in a predetermined direction at a predetermined velocity, in synchronization with which the reticle stage is scanned at a scanning velocity corresponding to the predetermined velocity of the wafer stage. Further, positional discrepancy amounts of the both stages in the scanning direction and the non-scanning direction (direction perpendicular to the scanning direction) are determined by arithmetic operation. The position of, for example, the reticle stage is finely adjusted so that the determined positional discrepancy amounts are decreased.
In the conventional technique as described above, the positional discrepancy amounts in the scanning and non-scanning directions are determined for the reticle stage and the wafer stage during scanning exposure, and control is performed so that the determined positional discrepancy amounts are independently corrected. Therefore, for example, even when the wafer stage is rotated by yawing during scanning exposure, the positional discrepancy amounts are independently corrected in the scanning direction and the non-scanning direction, resulting in an inconvenience that a positional discrepancy arises between the reticle and the wafer.
In order to overcome the inconvenience, it can be thought that a relative angle of rotation between the reticle stage and the wafer stage is also detected to control the angle of rotation into a predetermined target value. However, when the positional discrepancy amount in the translational direction and the discrepancy amount in the angle of rotation are corrected independently with each other, an inconvenience arises in that the process takes a long following time until the positional discrepancy amounts in the translational direction and in the rotational direction become allowable values or less respectively because of occurrence of another positional discrepancy amount in the translational direction due to rotation.
On the other hand, as the velocity of the stage becomes higher, a problem arises in relation to discrepancy in synchronization between the both stages resulting from a time lag during measurement by position sensors. For example, as for an apparatus which uses a laser interferometer as a position sensor, a time lag of several tens .mu.sec arises between an actual movement position of a stage and a result of measurement for its position due to a signal processing time in a light-receiving element and a circuit (for example, an analog circuit of a sensor amplifier). If the influence exerted by the time lag is identical with respect to all sensors, then no influence is exerted on synchronous control. However, actually, the time lag is different with respect to each of sensors (dispersion exists between sensors) in almost all cases. Accordingly, discrepancy in synchronization occurs between the reticle stage and the wafer stage, resulting in an inconvenience that the occurrence of discrepancy in synchronization makes a cause of exposure failure. The faster the velocity of the stage is, the larger the positional discrepancy due to the discrepancy in synchronization is.